Phased array transmission lens feed system



Aug. 11, 1970 P. SAFRAN PHASED ARRAY TRANSMISSION LENS FEED SYSTEM Filed Jan. 9, 1968 FlG. 1

PAUL. fiAFPA/U PUG. 5

United States Patent US. Cl. 333-6 13 Claims ABSTRACT OF THE DISCLOSURE A phased array transmission lens fed by a parallel plate section spaced from the lens to form a Wave guide. Couplers attached to phase shifters in the lens extend into the Wave guide. Multiple inputs are provided for monopulsing.

BACKGROUND OF TI-IE INVENTION This invention relates to electronically scanned radar antenna systems, and in particular to a parallel plate feed for a transmission type electronically scanned antenna.

Modern requirements of high data rates, high target densities, and multiple function scanning have dictated the use of electronically scanned radar in a number of applications. Particularly in mobile tactical applications, such as use in jet aircraft, size and weight limitations are critical.

Illustrative examples of conventional electronically scanned antennas and their modes of operation are shown and described in Sperry Engineering Review, Winter, 1965, and in Boeing Document D2-82590-1, and in the references cited therein.

The most common electronically scanned antenna system employs an array of phase shifters, each phase shifter being attached to a radiating element for forming an antenna beam. The radiating elements are energized through the phase shifters by means of a feed system. Two types of feed systems, direct (confined) and optical (space) feeds, have been employed. Direct feeds, fabricated in wave guide, coaxial line, or strip line, may be of a variety of basic types, such as corporate feed, parallel feed, series feed and various matrices. All suffer from excessive complexity and weight in an antenna large enough to meet normal operational requirements. The depth of the feed system also significantly increases the volume of the antenna. Optical feeds utilize a horn spaced from the lens. Energy dispersed from the horn is collected by pick-up radiators connected to the phase shifters. The phase shifters collimate the incident spherical wave front from the feed into a planar phase front, or into a nonplanar phase front to vary the beam shape. This phase front is tilted to scan the beam. The lens may be of either the reflection or the transmission type, but in either case the feed horn must be spaced from the lens. Furthermore, the feed horn must be held in a precisely determined position relative to the lens. These requirements add considerably to the complexity, weight and volume of the antenna system.

One of the objects of this invention is to provide a feed system for an electronically scanned antenna which does not add significantly to the volume of the array.

Another object is to provide such a feed system which is simple and light, and which is virtually self-supporting.

Other objects will occur to those skilled in the art in the light of the following description and accompanying drawing.

SUMMARY OF THE INVENTION In accordance with this invention, generally stated, a feed system is provided for a phased array transmission 3,524,151 Patented Aug. 11, 1970 lens which includes a plate section parallel with and spaced from the rear face of the lens to form a wave guide with the rear face of the lens. The parallel plate is conveniently substantially congruent with the rear face of the lens. A propagating means connected to the parallel plate introduces an electromagnetic wave front into the wave guide section. Couplers or probes connected to the phase shifters in the lens couple the wave to the phase shifters. Each coupler is proportioned to give a coupling coefiicient which extracts sufficient power to give the desired amplitude taper.

In the preferred embodiment the parallel plate is attached to the rear face of the lens by a gasket around its outer periphery, at a distance from the rear face of the lens of less than a wave length of the dominant frequency of the propagating wave.

Also in the preferred embodiment the propagating means are a point source or a set of point sources of electromagnetic excitation. The Wave guide thus acts as a radial wave guide and produces a cylindrical wave front or set of cylindrical wave fronts. Also in the preferred embodiment the propagating mode is T EM, and therefore the propagating means and couplers are both of the stub type and the spacing between the parallel plate and the rear face of the lens is very small, on the order of a small fraction of a wave length.

In another embodiment the propagating means are a set of slotted rectangular wave guides, and the propagating mode is TE (rotated from TEM). The couplers are therefore of the loop type, and the spacing of the parallel plate from the rear face of the lens is on the order of three quarters of a wave length.

BRIEF DESCRIPTION OF THE DRAWING In the drawings, FIG. 1 is a view in perspective partially cut away, of an antenna system including one illustrative embodiment of feed system of this invention;

FIG. 2 is a diagrammatic view in section, taken along the line 22 of FIG. 1;

FIG. 3 is a view in perspective of an antenna system including another embodiment of feed system of this invention; and

FIG. 4 is a view in perspective of an antenna system including another embodiment of feed system of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and in particular to FIGS. 1 and 2, reference numeral 1 indicates one illustrative embodiment of feed system of this invention. The feed system 1 includes a propagating means 2 comprising a cable 3, into the end of which is embedded a stub probe 4. The propagating means 2 is mounted at the center of a plate 5 with the stub probe 4 extending through the plate 5. The plate 5 is attached to a lens 6, and spaced from it to form a gap 19, by a gasket 7 extending around the periphery of the plate 5 and the lens 6. The width of the gap 19 is a small fraction of a wave length of the dominant frequency to be propagated, proportioned according to standard wave guide engineering principles for TEM mode waves. The inner surface 8 of the gasket 7 is made of a lossy material which will absorb any energy which reaches it from the propagating means 2. The lens 6 includes a supporting structure 9 containing a large number of phase shifters 10. The rear face of the lens 6 is enclosed by a fiat closure plate 11. Stub probes 12 connected to the phase shifters 10 extend through the closure plate 11 into the gap between the closure plate 11 and the parallel plate 5. The stub probes 12 are proportioned to extract power according to the desired amplitude taper. The precise coupling coeflicient chosen depends not only on the distance of the probes from the center but also on the extent to which space tapering has been employed in arranging the phase shifters As shown in FIG. 2, an excitation of the propagating probe 4 produces a cylindrical TEM mode electromagnetic wave front 13. As the wave 13 travels outward cylindrically, it is coupled to the phase shifters 10 by the probes 12. Each phase shifter 10 shifts the phase of the electromagnetic Wave passing through it in response to a phase shifter driver 14 controlled by a computer 15. Each phase shifter setting includes a collimation factor compensating for the proximity of the phase shifter to the propagating probe 4 and a second factor for giving the desired phase taper. Thus, the phase shifters translate a cylindrical wave front to a planar wave front and then tilt the planar wave front to give the desired beam direction. Of course, a third factor may be added to distort the plane wave front for beam shaping.

It will be seen that, in effect, an optical feed is provided in which f/d (focal length over aperture diameter) is essentially zero, and therefore the spherically propagated wave front of the usual optical feed has been projected to a cylindrical wave front. The parallel plate feed thus yields the electrical advantage of an optical feed over a direct feed that if digital phase control is used the collimation correction randomizes the phase errors due to phase quantization and prevents the build up of high side lobes even when used with fewer control bits in each digital phase shifter. It is also lighter, more compact and physically simpler than either an optical feed with its requisite support structure or a direct feed.

Another illustrative embodiment of feed system of this invention is shown in FIG. 3. An elliptical transmission lens 26 is fed by a congruent parallel plate feed system 21 having an elliptical plate section 25 spaced from the lens 26 to form a gap 39 of the same width as thegap 19 in the embodiment shown in FIGS. 1 and 2. The lens 26 is identical in every respect except shape (and therefore precise configuration of phase shifters) with the lens 6 of the embodiment shown in FIGS. 1 and 2. A seal' 27 spaces the feed system 21 from the lens 26 and supports the feed system 21. Additional seals 34 divide the gap between the plate 25 and the rear face of the lens 26 into quadrants. Propagating means 22, identical with the propagating means 2 of the embodiment shown in FIGS. 1 and 2, are provided in each quadrant at a position adapted to optimize the illumination of that quadrant. The propagating means 22 are connected to each other by a standard monopulsing circuit 35. The monopulsing circuit 35 includes three standard channels; a sum channel 36, an elevation difference channel 37 and an azimuth difference channel 38. This arrangement allows standard monopulsing techniques to be used in a search and track type radar system.

Another illustrative embodiment of feed system of this invention is shown in FIG. 4. A parallel plate is spaced from a rectangular transmission lens 46 by a peripheral seal 47 and quadrant seals 54. Loop type probes 52 connected to phase shifters in the lens 46 extend into the gap 59 between the lens 46 and the parallel plate 45. Each quadrant is fed by propagating means 42 comprising a rectangular wave guide 43 having slots 44 which extend through the plate 45 and radiate into the gap 59. Terminations 60 are provided at the outer ends of the wave guides 43. The propagating means 42 are thus analogs of a direct series feed. The four wave guides 43 are positioned to optimize the elevation illumination. The coupling coefficients of the wave guide slots 44 are chosen to optimize the azimuth illumination. The input in this embodiment is adapted to be in the TB mode, and thus the parallel plate 45 is spaced from the lens 46 by a distance of approximately three quarters of a wave length of the dominant frequency to be propagated, proportioned according to standard wave guide engineering principles for TE mode wa es. Attached to the propagating means 42 is a standard monopulsing circuit 55 having the usual three channels: a sum channel 56, an elevation difference channel 57, and an azimuth difference channel 58.

Numerous variations in the feed system of this invention, within the scope of the appended claims, will occur to those skilled in the art. For example, separable sum and difference illuminations may be provided to optimize the monopulse characteristics, with or without quadrant partitions. Polarization-diverse feeds may be used to provide a polarization insensitive feed. The rear face closure plate on the lens may be eliminated if the phase shifters are placed close enough to each other and in such a manner as to obviate wave leakage. Other propagating means may be used for propagating electromagnetic waves in the wave guide formed by the rear face of the lens and the parallel plate. Other couplers including slots may be used, and may be particularly desirable if other propagating modes are employed. These variations are merely illus trative.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is;

1. A feed system for energizing a phased array transmission lens having a plurality of controllable phase shifters, a rear face, and couplers arranged in at least two dimensions over substantially the entire surface of said rear face, said couplers being connected to said phase shifters for coupling electromagnetic waves to said phase shifters through said rear face, comprising a plate spaced from said rear face to form a wave guide defined by said plate and said rear face, and propagating means for propagating electromagnetic Waves in said wave guide parallel to said plate and said rear face.

2. The feed system of claim 1 wherein said couplers extend through said rear face into said wave guide.

3. The feed system of claim 1 wherein said plate is spaced from said lens by a gasket extending around the periphery of said wave guide.

4. The feed system of claim 1 wherein said plate is substantially congruent with said rear face.

5. The feed system of claim 1 wherein said propagating means comprise a stub probe mounted on said plate and extending into said wave guide.

6. The feed system of claim 1 wherein said propagating means comprise a slotted wave guide mounted on said plate.

7. The feed system of claim 1 wherein said propagating means comprise a plurality of separate wave propagators, said separate wave propagators being connected by a circuit.

8. The feed system of claim 7 including seal means in said wave guide between at least two of said separate wave propagators.

9. The feed system of claim 1 wherein said rear face comprises a closure plate parallel to said plate spaced from said rear face.

10. The feed system of claim 1 wherein said rear face and said plate are planar.

11. The feed system of claim 1 wherein said rear face and said closure plate are spaced apart a distance less than one wave length of a dominant frequency of said electromagnetic Waves propagated in said wave guide.

12. A phased array transmission lens antenna system comprising a phased array transmission lens having a plurality of electronically controllable phase shifters, a rear face, and couplers arranged in at least two dimensions over substantially the entire surface of said rear face connected to said phase shifters for coupling electromagnetic waves to said phase shifters through said rear face; a feed system comprising a plate spaced from said rear face to form a wave guide defined by said plate and said rear face and propagating means for propgating electromagnetic waves in said wave guide, said propagating means comprising at least one point source of electromagnetic excitation at a dominant frequency for pro- 6 ducing a cylindrical wave front traveling parallel to said References Cited plate and said rear face about said point source; driver UNITED STATES PATENTS means for controlling said phase shifters, and computer means for controlling said driver means, said computer 2,566,703 9/ 1951 Iams 343-755 means and said driver means being adapted to cause said 3,170,158 2/1965 RQtman phase shifters to translate said cylindrical wave front to 5 3,245,081 4/ 1965 McFarland 343755 a substantially planar wave front and to tilt the planar wave front to give a desired beam direction. ELI LIEBERMAN Pnmary Exammer 13. The antenna system of claim 12 wherein said plate U S C1 X R and said rear face are spaced apart a distance less than 10 343 754 771 854 one wave length of said dominant frequency. 

